The present invention concerns an apparatus or plant for the treatment of liquids, particularly for the separation of solid and/or liquid particles from a liquid, which particles can have a smaller or greater specific gravity than that of the liquid. Although the invention is not so restricted, it is particularly concerned with such separation taking place in a basin of cylindrical shape or polygonal cross-section and having a vertical axis of symmetry. The basin includes a pre-sedimentation space and a single-step or multi-step separation space, taken in the direction of flow of the liquid to be treated.
The invention furthermore concerns a lamellar (i.e. laminated multi-layer thin plate) construction serving for the above-mentioned liquid treatment purposes having channels, the axes of which are oriented in mutually parallel directions and which serve to separate solid and/or liquid particles from a liquid in liquid treatment plants or apparatus.
In the present invention, "liquid treatment" means in general purification of liquids e.g. purification or decontamination of effluents, in the course of which the liquid is separated from another liquid or from solid matter, or wherein the liquid is brought into contact with a gas or air, or wherein the liquid is subjected to a biological treatment. Also, "liquid treatment" is intended to include the cooling and degassing or de-aerating of liquids.
Modern water and effluent purification technologies have throughout the world required the establishment of modern liquid separation systems, such as sedimentation systems, to enable modern environmental protective plants to be provided.
Numerous plants and equipments are known for the fundamental task of separating particulate and/or suspended solid materials from liquids. One type of such plant consists of apparatus having a vertical axis and a circular or polygonal cross-section, made e.g. from prefabricated concrete rings in the manner of a well shaft.
In known circular well-like apparatus, used principally for small capacity petroleum oil or sand catchment basins, or for presedimentation or final sedimentation basins, there is essentially a single working space of cylindrical shape wherein the efficiency of the separation process, such as sedimentation, is relatively restricted. Such equipment does not permit separation processes, such as sedimentation to be optimized. This is because their efficiency is restricted and because of their large size their space requirements are large and hence they are uneconomical.
It is fundamental that separating equipment such as sedimentation devices should, as far as possible, eliminate turbulent flow conditions. From the point of view of sedimentation, use of laminar flow is a basic requirement to ensure that the suspended materials, particles and grains settle out undisturbed.
Laminar flow and turbulent flow can be distinguished by utilizing the Reynolds number. The Reynolds number should be less than 500, under optimal conditions, to ensure that sedimentation takes place during laminar flow.
Hitherto known separating basins of circular section have numerous other disadvantages. The liquid flow conditions in such devices are unfavourable as the flow is turbulent. Furthermore, one cannot obtain axially symmetrical radial flow in these known, small units and therefore the enhanced effects which might be available to be obtained from such flow conditions cannot be exploited. An example of such an enhanced effect is the possibility of radial flow between the so-called coalescent (drop-forming and coalescing) plates which in the case of separation of e.g. oily effluents provides considerable improvement in efficiency.
The invention seeks to ensure laminar flow conditions in complex separation processes taking place in currently known, circular-section, annular or polygonal section separation devices by the use of lamellar (laminar multi-plate) sedimentation systems. A further aim of the invention is to increase the efficiency of existing separation plants, e.g. in the case of oily effluents, to increase the efficiency of drop formation, and in general the invention seeks to eliminate, or at least to reduce, the disadvantages of known single-space circular-section or annular sedimentation basins, both from the point of view of efficiency and economy.
The invention also aims at achieving greater separation efficiency in known separation systems with a smaller plant in order to reduce the space or land area requirements while also reducing the investment and running costs.
The above-mentioned disadvantages become more evident in sedimentation basins of radial throughflow provided with mobile (circularly moving) sludge dredgers. This is because in such plants one cannot use fixed-position multi-plate lamellar elements because of the path of movement and construction of the mobile dredger.
There are additional disadvantages with radial through-flow sedimentation basins having mobile dredgers, namely that secondary flow patterns are set up and these have a disadvantageous influence on the hydraulic and technological efficiency.
Secondary flow can also be produced e.g. by the temperature differences in the effluent or raw waters, which temperature difference can be as low as 1.degree.-2.degree. C. and in such cases the secondary flow entrains the particles in the course of their settling out and conveys them to the upper layers of the basin, whereby the sedimentation process is slowed down and a significant proportion of the suspended matter exits in the discharged water. Another disadvantageous influence on flow conditions in known radial through-flow basins is due to winds which significantly modify flow conditions in the vicinity of the water surface. This factor is significant primarily in the larger diameter sedimentation plants such as the Dorr-type basins wherein the water surface can deviate from the horizontal by several millimeters under the effect of wind. As a consequence, the loading of the discharge weir is unfavourable because this loading varies from point to point along the perimeter of the unit and this is very unfavourable from the point of view of distribution of residence times.
Similarly, disadvantageous effects can be exerted by certain movable constructional elements of the dredgers as well as baffles and underwater walls which can produce undesired flow patterns and dead spaces.
Accordingly, a further aim of the invention is to ensure laminar flow conditions in hitherto known circular or polygonal section sedimentation basins provided with mobile dredgers while eliminating or reducing the above-mentioned disadvantages and improving efficiency, as well as other parameters of economy. The invention thus aims at reducing the size of the plant thereby decreasing the investment costs, running costs and the land area requirements.